With the increasing demand of users for radio access rate, WLAN emerges as the time require, for it can provide a fast wireless data access within a relatively small region. WLAN involves various kinds of techniques, one of the most extensively used technical standard of which is IEEE 802.11b, whose frequency band is 2.4 GHz with data transmission rate up to 11 Mbps. Other technical standards using the same frequency band include IEEE 802.11g and Bluetooth, wherein the data transmission rate of IEEE 802.11g is up to 54Mbps. Other new standards of WLAN, such as IEEE 802.11a and ETSI BRAN Hiperlan2, use the frequency band of 5 GHz, with the transmission rate up to 54 Mbps as well.
Although WLAN involves various kinds of wireless access techniques, most WLAN techniques utilize IP data packets for data transmission. The specific WLAN access technique is usually transparent to the upper IP level in a wireless IP network which is usually configured with Access Points (AP) for UE radio access, and with controlling and connecting devices for IP data transmission.
Along with the appearance and development of WLAN, the inter-working of WLAN with various mobile communication networks, such as GSM, Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA), Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) and CDMA2000 has become the focus of researches. These WLAN interworked with mobile communication networks are called interworking WLAN. And interworking WLAN and mobile communication networks connected with it constitute WLAN interworking networks. Typical WLAN interworking network includes 3GPP-WLAN interworking network defined by 3GPP, 3GPP2-WLAN interworking network defined by 3GPP2, and so on. In accordance with 3rd Generation Partner Project (3GPP) standards, via the access network (AN) of a WLAN, a UE is able to connect with not only Internet or Intranet, but the home network or visited network of a 3GPP system. More specifically, and when a WALN UE roams, it will be connected with the 3GPP visited network via the WLAN AN. A part of entities of the 3GPP visited network interworks with its corresponding entity of the 3GPP home network respectively, for example, as shown in FIG. 1, 3GPP Authentication, Authorization and Accounting (AAA) Agent in a 3GPP visited network interworks with 3GPP AAA Server in the 3GPP home network; WLAN Access Gateway (WAG) of the 3GPP visited network interworks with Packet Data Gateway (PDG) of the 3GPP home network, and etc. When a WLAN UE accesses in non-roaming case, it will be connected with the 3GPP home network via the WLAN AN, as shown in FIG. 2. FIG. 1 is a schematic diagram illustrating the architecture of the networking of a WLAN system and a 3GPP system in roaming case; while FIG. 2 is a schematic diagram illustrating the architecture of the networking of a WLAN system and a 3GPP system in non-roaming case.
As shown in FIG. 1 and FIG. 2, a 3GPP system primarily comprises Home Subscriber Server (HSS)/Home Location Register (HLR), 3GPP AAA Server/Proxy, WAG, PDG, Charging Gateway (CGw)/Charging information Collecting Function (CCF) and Online Charging System (OCS). WLAN UE, WLAN AN and all the entities of the 3GPP system together construct a 3GPP-WLAN interworking network, which can be used as a WLAN service system. In this service system, 3GPP AAA Server is in charge of the authentication, authorization and accounting for a WLAN UE, collecting the charging information sent from the WLAN AN and transferring the charging information to the charging system; PDG bears the burden of transmitting the user's data from the WLAN AN to the 3GPP network or other packet switching networks; and the charging system is in charge of receiving and recording the user's charging information transferred from the network, wherein OCS instruct the network to send online charging information periodically in accordance with the expenses of the online charged users, meanwhile making statistics and keeping it under control.
Except for roaming, when a WLAN UE desires to access the Internet/Intranet directly, it has access to the Internet/Intranet via the WLAN AN after accomplishing the accessing authentication process with AAA server (AS). If the WLAN UE desires to access services of 3GPP PS domain as well, it should further request for the service of Scenario 3 from the 3GPP home network, which is as follows: the WLAN UE initiates a Service Authentication Request to the AS of the 3GPP home network, the AS sends an Access Permission Message and assigns a corresponding PDG to the WLAN UE when the request is acceptable; after a tunnel between the WLAN UE and the assigned PDG is established, the WLAN UE gains access to the services of 3GPP PS domain. At the same time, CGw/CCF and OCS record the accounting information according to the network usage of the WLAN UE. Under the circumstances of roaming, when a WLAN UE desires to access the Internet/Intranet directly, it can request the 3GPP home network for accessing the Internet/Intranet via the 3GPP visited network. If the WLAN UE desires to access 3GPP PS domain and request for the service of Scenario 3 as well, it needs to initiate a Service Authentication procedure to the 3GPP home network via the 3GPP visited network. Similarly, this procedure will be carried out between the WLAN UE and the AS of the 3GPP home network. After the authentication, the AS assigns a corresponding home PDG to the WLAN UE, and after a tunnel between the WLAN UE and the assigned PDG is established via the WAG in the 3GPP visited network, the WLAN UE gets access to the services of 3GPP PS domain.
As shown in FIG. 3, in a 3GPP-WLAN interworking network, if a WLAN connects with a plurality of 3GPP visited networks, i.e. a plurality of Mobile communication Networks, simultaneously, where, the 3GPP visited network refers to a Visited Public Land Mobile Network (VPLMN), after accessing the WLAN, a WLAN UE needs to select a VPLMN to access. Take an example in China, a WLAN AN connects to a couple of VPLMN Operation Network of China Mobile and China Unicom at the same time, then after a user of China Unicom accesses the WLAN, it needs to indicate the WLAN AN that it needs to access the VPLMN Operation Network of China Unicom.
For another example, a French user roams to a WLAN of China, if its home network has roaming protocols with both China Mobile and China Unicom at the same time and the WLAN AN connects to both China Mobile and China Unicom, a accessing VLPMN needs to be selected, after the French user accesses the WLAN. Then, how does the WLAN UE select the network to be accessed, how does it inform the WLAN AN the network selection information, and how does a 3GPP-WLAN interworking network implement interactive process according to the network selection information. All of the above questions are resolved by the following scheme: the WLAN UE sends the network selection information to the WLAN AN through an Authentication Request, the WLAN AN identifies the mobile communication network which the WLAN UE desires to access according to the carried network selection information, and connects the current WLAN UE with the selected network to implement authentication and subsequent operations.
However, if the WLAN UE implements network selection every time it accesses, the network resource will be greatly consumed. For example, when a user roams to other places, the home mobile communication network of the user does not directly connect to the WLAN AN which the WLAN UE currently belongs to; if the WLAN UE carries its home network as an initial selected network to the WLAN AN each time the user accesses to the WLAN, a network selection procedure will be triggered. In this procedure, the WLAN network sends network selection information to the WLAN UE who will access a network after judging and selecting, which will consume the network resource and delay the access. However, for the WLAN UE who has accessed a new WLAN network, simply adopting the previously selected mobile communication network may not guarantee that the current selected network is an optimal PLMN network. In another word, when the WLAN UE switches to a new WLAN network, the default mobile communication network it accesses or a mobile communication network formerly selected is likely to be used, for there is a roaming relationship between the above mobile communication network and the home network of the WLAN UE. But the new WLAN network of the WLAN UE possibly has a direct connection with a Home Public Land Mobile Network (HPLMN) or some other better VPLMN. However, since there has been a default or selected mobile communication network to route, new network selection can not be implemented anymore, which means the WLAN UE can not be guaranteed to select an optimal PLMN network, such as a HPLMN, in the current WLAN.
How to guarantee a WLAN UE in a WLAN connected with a plurality of mobile communication networks to select a proper mobile communication network to access whenever the WLAN that the UE belongs to changes? A scheme is proposed, which makes use of the mobile communication network information of the last successful access as network selection information, and makes the current WLAN UE select an optimal mobile communication network to access; but since the above scheme is implemented by making use of the latest network selection results, if the judgment of whether the current WLAN changes is made based on the realization of an AP identity, i.e. the judgment is made whether the AP identity changes, the object of rapid access can not be obtained under the circumstances that the users frequently switch among APs.